| With the rapid development of MEMS technology,thick resist lithography technique which is used for large thickness and high aspect ratio films has been widely applied in the fields of mobile communications system,satellite navigation system,spaceflight and defence equipment.Because of convenient removal,good compatibility and small swelling in electroforming,positive thick resist is the first choice for making large thickness micro-mould and micro precision devices of cavity type.However,when the thickness of the resist is large in UV lithography,the dimensional accuracy of thick positive resist is extremely low,which restricts its application.Based on AZ50 XT resist,the factors having effect on the precision of positive thick resist were studied and the method of multiple exposure and development was proposed to make high-precision photolithography.Finally,based on this method,an integrated RF coaxial transmission line was made with lithography technology and electrochemical deposition technology.The main research contents and results are as follows:(1)Study on lithography accuracy of AZ50 XT resist.High absorption coefficient of AZ50 XT,inhomogeneity of the film and diffraction effect of light are the important factors that affect the precision of AZ50 XT.The combination of three factors lead to uneven distribution of exposure dose within the resist and low accuracy of lithography.The optical absorption measurement experiment and lithography experiment prove that large light absorption coefficient of AZ50 XT is the most important factor that affects lithography accuracy.(2)According to the influence factors of low accuracy of AZ50 XT lithography,the method of controlling the resist thickness by pre-exposure datum is adopted to reduce the edge bead effect and diffraction effect of light.And the method of multiple exposure and development based on back alignment is adopted to improve the distribution of exposure dose within the resist.Based on the theory of scalar angular spectrum diffraction,a light intensity simulation experiment is conducted to verify the effectiveness of this method.And the improvement of lithography accuracy is studied by multiple exposure and development experiments.The experimental results show that the method of multiple exposure and development can significantly improve the dimensional accuracy of AZ50 XT resist and the accuracy of the lithography pattern is no related to the mask size.Within a certain range,prolong the soft-bake time of multiple exposure and development can further improve the lithography precision.When the soft-bake time is extended to 3 hours,the average difference between top and bottom linewidth of lithography pattern is 4.7?m and the sidewall average inclination is 87.9°.(3)Based on the above experiment results,a kind of passive coaxial transmitter is fabricated by UV lithography technology with positive and negative photoresist and electrodeposition technology.The overall dimension is 3000?m×400?m×200?m,the maximum height of single layer is 60?m and the sidewall inclination of each layer is more than 85°.Aiming at low dimensional accuracy of thick positive photoresist AZ50 XT,the method of multiple exposure and development is proposed to make high-precision electroforming mask.Aiming at poor binding force between inner conductor and supports during stripping,the method of sputtering layer graphical by removing extra sputtering layer is adapted to guarantee the binding properties of inner conductor and support.Aiming at the difficulty of detecting removal effect of resist inside the transmission line,the method of detecting by wettability test about different concentration of ethanol water solution is proposed.The lithography mask is designed by the method of size error compensation,and precision of inner conductor and dielectric cavity is measured.The measurement results show that the error of inner conductor is within ±2?m and the height error of the single dielectric cavity within +2.5?m. |
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